Yeah I remember a yellow cabriolet with one in. Had a pretty awful kit etc. I never looked at it closely but was told it looked a bit sketchy.

I've heard that the Duratec V6 only weights about the same as the RS2000 engine as it is alloy but, due to it's layout, the weight position wouldn't be ideal.

I think if you want to do something different, try fitting a 2.0 Duratec. It could be made to fit nicely, is all-alloy so lighter than a Zetec, and really tunable. Could make for a good car with one of them.